Epoxy resins have low reaction shrinkage, excellent electrical, mechanical properties, and high processability and chemical resistance, and are used as a matrix and coating for electric, electronic, construction, and composite materials. For example, epoxy resins are used for encapsulation of semiconductor devices, adhesive films, insulating resin sheets such as prepregs, circuit boards, solder resists, underfills, die bonding agents, and component replenishing resins.
Generally, such an epoxy resin is used after being mixed with a curing agent to be a thermosetting material rather than being used alone. Here, since properties of the epoxy resin depend on a three-dimensional structure created after curing, selection of the curing agent is important. Although many curing agents for epoxy resins have been developed, a curing catalyst is used together in order to catalyze curing reaction. In an apparatus using an epoxy resin composition, there is a need for a curing agent having low temperature curability that allows the rein composition to be cured at low temperature for enhancement of productivity and high storage stability that catalyzes curing only at a desired temperature while not exhibiting catalytic activity at other temperatures for improvement of handling performance during distribution and storage. Since an adduct of triphenylphosphine and 1,4-benzoquinone, as a curing catalyst, catalyzes curing even at relatively low temperatures, there are problems in that, when an epoxy resin composition is mixed with other components before curing, the epoxy resin composition is partially cured by heat generated from the mixture system or externally applied heat, and in that after completion of mixing, the epoxy resin composition can undergo curing even during storage at room temperature and thus has poor storage stability. Such curing can cause the epoxy resin composition to exhibit increase in viscosity and deterioration in flowability when the epoxy resin composition is liquid, and can cause the epoxy resin composition to exhibit viscosity when the epoxy resin composition is solid, and such a state change is not uniform within the epoxy resin composition. As a result, when the epoxy resin composition is actually cured at high temperature, the epoxy resin composition can suffer from deterioration in moldability due to deterioration in flowability, and can cause deterioration in mechanical, electrical and chemical properties of a molded article. In the related art, Korean Patent No. 10-0290448 discloses an epoxy resin curing catalyst which is a carboxylate of a bicyclic amidine.